Almost all aircraft are equipped with exterior light units. In particular, large passenger air planes are provided with a wide variety of exterior light units. The exterior light units are provided for a wide variety of different purposes, such as for allowing the passengers and/or air crew to view the outside, for passive visibility, for signalling purposes, etc. Examples of such exterior light units are navigation lights, also referred to as position lights, beacon lights, anti-collision lights, wing scan lights, landing lights, taxi lights, runway turn-off lights, etc.
Exterior aircraft light units are exposed to very hazardous conditions. They have to withstand large aerodynamic forces as well as large temperature variations. In particular, both very low temperatures, due to the high cruising altitude, as well as very high temperatures, due to turbine exhaust, may potentially be present in the environment of exterior aircraft light units. Operation at extreme temperatures may be detrimental to the aging of LEDs, employed in modern exterior aircraft light units.
In order to observe the aging of the employed LEDs, some exterior aircraft light units are equipped with sensors for determining a light output level of the employed LED(s). This observation of the light output level is often also referred to as near end of life detection, because such light units generate a near end of life signal, indicating that the LED(s) has/have reached or is/are soon to reach their maximum life time. As a response to this signal, the light sources of the exterior aircraft light units or the entire exterior aircraft light units may be replaced. Near end of life detection requires some of the light, emitted by the light source(s), to not contribute to the amount of light that exits the exterior aircraft light unit and forms the output light intensity distribution. Prior art exterior aircraft light units are not satisfactory in terms of the inclusion of the near end of life detector.
Accordingly, it would be beneficial to provide an exterior aircraft light unit with an improved inclusion of a near end of life detector. Further, it would be beneficial to provide an aircraft with such an exterior aircraft light unit.